3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone derivatives of formula I: ##STR3## are known compounds. The free base form of the compound is known to be a highly effective antiallergic agent for oral administration. The antiallergic agent is now under clinical evaluation. U.S. Pat. No. 4,419,357 and Journal of Medical Chemistry, pp. 2403-1409, Vol. 29, 1986 disclosed a process for preparing the compound in free base form by reaction of o-nitrobenzoyl chloride with 5-amino-tetrazole followed by hydrogenation, cyclization and finally forming sodium salt through reaction with sodium hydroxide. The yield of the process is only about 23%. The process comprises four steps and requires hydrogenation equipment and therefore is very costly.